Selective TAAR1 agonists induce conditioned taste aversion

TAAR1 agonists improve glycemic control, reduce body weight and modulate neurocircuits governing energy balance and feeding

OBJECTIVE

Metabolic Syndrome, which can be induced or exacerbated by current antipsychotic drugs (APDs), is highly prevalent in schizophrenia patients. Recent preclinical and clinical evidence suggest that agonists at trace amine-associated receptor 1 (TAAR1) have potential as a new treatment option for schizophrenia. Intriguingly, preclinical tudies have also identified TAAR1 as a novel regulator of metabolic control. Here we evaluated the effects of three TAAR1 agonists, including the clinical development candidate ulotaront, on body weight, metabolic parameters and modulation of neurocircuits implicated in homeostatic and hedonic feeding.

METHODS

Effects of TAAR1 agonists (ulotaront, RO5166017 and/or RO5263397) on body weight, food intake and/or metabolic parameters were investigated in rats fed a high-fat diet (HFD) and in a mouse model of diet-induced obesity (DIO). Body weight effects were also determined in a rat and mouse model of olanzapine-, and corticosterone-induced body weight gain, respectively. Glucose tolerance was assessed in lean and diabetic db/db mice and fasting plasma glucose and insulin examined in DIO mice. Effects on gastric emptying were evaluated in lean mice and rats. Drug-induced neurocircuit modulation was evaluated in mice using whole-brain imaging of c-fos protein expression.

RESULTS

TAAR1 agonists improved oral glucose tolerance by inhibiting gastric emptying. Sub-chronic administration of ulotaront in rats fed a HFD produced a dose-dependent reduction in body weight, food intake and liver triglycerides compared to vehicle controls. In addition, a more rapid reversal of olanzapine-induced weight gain and food intake was observed in HFD rats switched to ulotaront or RO5263397 treatment compared to those switched to vehicle. Chronic ulotaront administration also reduced body weight and improved glycemic control in DIO mice, and normalized corticosterone-induced body weight gain in mice. TAAR1 activation increased neuronal activity in discrete homeostatic and hedonic feeding centers located in the dorsal vagal complex and hypothalamus with concurrent activation of several limbic structures.

CONCLUSION

The current data demonstrate that TAAR1 agonists, as a class, not only lack APD-induced metabolic liabilities but can reduce body weight and improve glycemic control in rodent models. The underlying mechanisms likely include TAAR1-mediated peripheral effects on glucose homeostasis and gastric emptying as well as central regulation of energy balance and food intake.

Robust aversive effects of trace amine-associated receptor 1 activation in mice

Drugs that stimulate the trace amine-associated receptor 1 (TAAR1) are under clinical investigation as treatments for several neuropsychiatric disorders. Previous studies in a genetic mouse model of voluntary methamphetamine intake identified TAAR1, expressed by the Taar1 gene, as a critical mediator of aversive methamphetamine effects. Methamphetamine is a TAAR1 agonist, but also has actions at monoamine transporters. Whether exclusive activation of TAAR1 has aversive effects was not known at the time we conducted our studies. Mice were tested for aversive effects of the selective TAAR1 agonist, RO5256390, using taste and place conditioning procedures. Hypothermic and locomotor effects were also examined, based on prior evidence of TAAR1 mediation. Male and female mice of several genetic models were used, including lines selectively bred for high and low methamphetamine drinking, a knock-in line in which a mutant form of Taar1 that codes for a non-functional TAAR1 was replaced by the reference Taar1 allele that codes for functional TAAR1, and their matched control line. RO5256390 had robust aversive, hypothermic and locomotor suppressing effects that were found only in mice with functional TAAR1. Knock-in of the reference Taar1 allele rescued these phenotypes in a genetic model that normally lacks TAAR1 function. Our study provides important data on TAAR1 function in aversive, locomotor, and thermoregulatory effects that are important to consider when developing TAAR1 agonists as therapeutic drugs. Because other drugs can have similar consequences, potential additive effects should be carefully considered as these treatment agents are being developed.